CN108419033B - HDR image sensor pixel structure based on inflection point and imaging system - Google Patents
HDR image sensor pixel structure based on inflection point and imaging system Download PDFInfo
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- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
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- H04N25/57—Control of the dynamic range
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- H—ELECTRICITY
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- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
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- H—ELECTRICITY
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- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/71—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
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Abstract
The invention discloses an HDR image sensor pixel structure based on an inflection point and an imaging system, wherein a reset transistor of the pixel structure is coupled between a floating diffusion node and a first voltage source, and a photodiode of the pixel structure is coupled to the floating diffusion node through a rolling exposure transmission unit and a global exposure transmission unit respectively; the rolling exposure transfer unit may be used to provide a balancing current during exposure of the photodiode to control the full well charge amount. The pixel structure of the present invention can support multiple exposure modes because two exposure mode transfer units can be used to transfer charges, and the rolling exposure transfer unit can be used to provide balance current to control the full-well charges during the exposure of the photodiode, and change the signal transfer gain, so that the pixel structure has high dynamic range characteristics.
Description
Technical Field
The invention relates to the technical field of image sensors, in particular to an HDR image sensor pixel structure based on an inflection point and an imaging system.
Background
In recent years, the CMOS image sensor industry has been rapidly developed, the chip area of the image sensor has been becoming smaller, and as the pixel size has been reduced, the demand for the image sensor to perform in a wide range of lighting conditions (ranging from low-light conditions to bright-light conditions) has become more difficult to achieve. This performance capability is commonly referred to as having high dynamic range imaging (HDR). In conventional image capture devices, a pixel cell requires multiple successive exposures to achieve HDR.
In order to improve the dynamic range of the image sensor, various new pixel unit structures are proposed, however, the existing various pixel unit structures can only support a single exposure mode generally, thereby limiting the application scenarios of the pixel unit.
Thus, there is a need for an improved pixel structure for HDR image sensors.
Disclosure of Invention
The invention aims to provide an HDR image sensor pixel structure based on an inflection point and an imaging system, so as to solve the problem that the conventional pixel structure cannot support multiple exposure modes.
In order to solve the technical problems, the invention adopts the following technical scheme:
an inflection point based HDR image sensor pixel structure, comprising:
a photodiode for accumulating charges generated by a photoelectric effect in response to incident light;
a reset transistor coupled between a first voltage source and the floating diffusion node for resetting a voltage of the floating diffusion node according to a reset control signal;
a rolling exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the rolling exposure transmission unit is used for providing balance current to control the full-trap charge and change the transmission gain in the exposure process of the photodiode; and for transferring charge accumulated by the photodiode to the floating diffusion node in a rolling exposure mode or a hybrid exposure mode;
a global exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the global exposure transmission unit is used for storing the electric charge accumulated by the photodiode in the exposure process of a global exposure mode or a mixed exposure mode and transferring the stored electric charge to the floating diffusion node after the exposure is finished;
and the output unit is coupled to the floating diffusion node and used for amplifying and outputting the voltage signal of the floating diffusion node.
In one embodiment of the present invention, the rolling exposure transfer unit includes a rolling exposure transfer transistor, and the photodiode is coupled to the floating diffusion node through the rolling exposure transfer transistor.
In an embodiment of the present invention, the rolling exposure transfer transistor is configured to operate in a sub-threshold state as the terminal voltage of the photodiode gradually decreases during the exposure of the photodiode, so as to provide a current to the photodiode to balance the photocurrent, so that the terminal voltage of the photodiode is kept constant.
In one embodiment of the present invention, the global exposure transfer unit includes a global exposure transfer transistor, an exposure control transistor, and a storage capacitor, the photodiode is coupled to the floating diffusion node through the exposure control transistor and the global exposure transfer transistor, a first terminal of the storage capacitor is coupled to a node between the exposure control transistor and the global exposure transfer transistor, and a second terminal thereof is coupled to a gate or a ground terminal of the exposure control transistor or to a fixed voltage value.
In one embodiment of the present invention, the storage capacitor is a separate capacitance device or a parasitic capacitance of the exposure control transistor.
In one embodiment of the present invention, the hybrid exposure mode is a rolling exposure and global exposure alternating exposure mode.
In one embodiment of the invention, the first voltage source is a variable voltage source.
In one embodiment of the present invention, the output unit includes an amplifier coupled between a floating diffusion node and a column output line for amplifying and outputting a voltage signal of the floating diffusion node. In one embodiment of the present invention, the amplifier is a source follower transistor having a gate coupled to the floating diffusion node, a drain coupled to a second voltage source, and a source coupled to a column output line.
In one embodiment of the present invention, the output unit further includes a row selection transistor, and the amplifier is coupled to a column output line through the row selection transistor.
An imaging system comprising an array of pixels arranged in rows and columns, each pixel in the array of pixels comprising:
a photodiode for accumulating charges generated by a photoelectric effect in response to incident light;
a reset transistor coupled between a first voltage source and the floating diffusion node for resetting a voltage of the floating diffusion node according to a reset control signal; a rolling exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the rolling exposure transmission unit is used for providing balance current in the exposure process of the photodiode so as to control the charge amount of a full well and change the transmission gain; and for transferring charge accumulated by the photodiode to the floating diffusion node in a rolling exposure mode or a hybrid exposure mode;
a global exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the global exposure transmission unit is used for storing the electric charge accumulated by the photodiode in the exposure process of a global exposure mode or a mixed exposure mode and transferring the stored electric charge to the floating diffusion node after the exposure is finished;
and the output unit is coupled to the floating diffusion node and used for amplifying and outputting the voltage signal of the floating diffusion node.
In one embodiment of the present invention, the imaging system further includes a logic control unit, a driving unit, a column a/D conversion unit, and an image processing unit; wherein:
the logic control unit is used for controlling the working sequence logic of the whole system;
one end of the driving unit is connected with the logic control unit, and the other end of the driving unit is coupled with the pixel array and used for driving and controlling each control signal line in the pixel array;
the column A/D conversion unit corresponds to each column of pixels in the pixel array and is used for realizing analog/digital conversion of column signals under the control of the logic control unit;
the image processing unit is used for carrying out image processing on the image digital signals output by the column A/D conversion unit under the control of the logic control unit.
In one embodiment of the present invention, the driving unit includes:
a row driving unit, one end of which is connected with the logic control unit and the other end of which is coupled with the pixel array, and is used for providing corresponding row control signals for the pixel array;
and the column driving unit is connected with the logic control unit at one end, is coupled with the pixel array at the other end and is used for providing a corresponding column control signal for the pixel array.
In one embodiment of the present invention, the rolling exposure transfer unit includes a rolling exposure transfer transistor, and the photodiode is coupled to the floating diffusion node through the rolling exposure transfer transistor.
In an embodiment of the present invention, the rolling exposure transfer transistor is configured to operate in a sub-threshold state as the terminal voltage of the photodiode gradually decreases during the exposure of the photodiode, so as to provide a current to the photodiode to balance the photocurrent, so that the terminal voltage of the photodiode is kept constant.
In one embodiment of the present invention, the global exposure transfer unit includes a global exposure transfer transistor, an exposure control transistor, and a storage capacitor, the photodiode is coupled to the floating diffusion node through the exposure control transistor and the global exposure transfer transistor, a first terminal of the storage capacitor is coupled to a node between the exposure control transistor and the global exposure transfer transistor, and a second terminal thereof is coupled to a gate or a ground terminal of the exposure control transistor or to a fixed voltage value.
In one embodiment of the present invention, the storage capacitor is a separate capacitance device or a parasitic capacitance of the exposure control transistor.
In one embodiment of the present invention, the hybrid exposure mode is a rolling exposure and global exposure alternating exposure mode.
In one embodiment of the invention, the first voltage source is a variable voltage source. In one embodiment of the present invention, the output unit includes an amplifier coupled between a floating diffusion node and a column output line for amplifying and outputting a voltage signal of the floating diffusion node.
In one embodiment of the present invention, the amplifier is a source follower transistor having a gate coupled to the floating diffusion node, a drain coupled to a second voltage source, and a source coupled to a column output line. The second voltage source may be a fixed voltage source.
In one embodiment of the present invention, the output unit further includes a row selection transistor, and the amplifier is coupled to a column output line through the row selection transistor.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects:
1) the pixel structure of the image sensor provided by the invention adopts two exposure mode transmission units to transfer the charges accumulated after the exposure is finished, so that the pixel structure can support multiple exposure modes;
2) the pixel structure of the image sensor provided by the invention utilizes the rolling exposure transmission unit to provide the balance current in the exposure process of the photodiode so as to control the charge quantity of the full trap, so that the phenomenon of overexposure (blooming) caused by over-strong light intensity can be prevented, and the value of the full trap charge can be changed along with the change of the balance current and the light intensity, thereby realizing the characteristic of high dynamic range.
Drawings
Fig. 1 is a schematic structural diagram of a pixel structure of an HDR image sensor based on an inflection point according to an embodiment of the present invention;
FIG. 2a is a schematic timing control diagram of the pixel structure of FIG. 1 during an exposure period according to the present invention;
FIG. 2b is a graph showing the variation of output signals with light intensity under the exposure timing control shown in FIG. 2 a;
FIG. 3 is a timing diagram illustrating the pixel structure of FIG. 1 operating in a global exposure mode according to the present invention;
FIG. 4 is a timing diagram illustrating the pixel structure of FIG. 1 operating in a rolling exposure mode according to the present invention;
fig. 5 is a schematic structural diagram of a pixel structure of an HDR image sensor based on knee points according to another embodiment of the present invention;
fig. 6 is a schematic structural diagram of an imaging system according to an embodiment of the present invention.
Detailed Description
The following describes the pixel structure and the imaging system of the HDR image sensor based on knee point in further detail with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims. It is noted that the drawings are in greatly simplified form and that non-precision ratios are used for convenience and clarity only to aid in the description of the embodiments of the invention.
The invention provides an HDR image sensor pixel structure based on an inflection point, which comprises:
a photodiode for accumulating charges generated by a photoelectric effect in response to incident light;
a reset transistor coupled between a first voltage source and the floating diffusion node for resetting a voltage of the floating diffusion node according to a reset control signal;
a rolling exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the rolling exposure transmission unit can be used for providing balance current to control the full-trap charge and change the transmission gain during the exposure process of the photodiode; and operable to transfer charge accumulated by the photodiode to the floating diffusion node in a rolling exposure mode or a hybrid exposure mode;
a global exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the global exposure transmission unit can be used for storing the electric charge accumulated by the photodiode in the exposure process of a global exposure mode or a mixed exposure mode and transferring the stored electric charge to the floating diffusion node after the exposure is finished;
and the output unit is coupled to the floating diffusion node and used for amplifying and outputting the voltage signal of the floating diffusion node.
The image sensor pixel structure provided by the invention can support multiple exposure modes by arranging the two exposure mode transmission units to transfer charges under different exposure modes. And the rolling exposure transmission unit is utilized to provide balance current in the exposure process of the photodiode so as to control the charge quantity of the full trap, so that the phenomenon of overexposure (blooming) caused by over-strong light intensity can be prevented, and the value of the charge of the full trap can be changed along with the change of the balance current and the light intensity, so that the pixel structure can realize high dynamic range characteristic.
The embodiments of the present invention will be described in detail with reference to several specific examples.
Example 1
Referring to fig. 1, as shown in fig. 1, a pixel structure of an HDR image sensor based on knee point according to an embodiment of the present invention includes a photodiode pd for accumulating charges generated by photoelectric effect in response to incident light, the photodiode having a first terminal and a second terminal, the first terminal being connected to a ground terminal, the second terminal being respectively coupled to a floating diffusion node FD via two branches, one branch being a rolling exposure transfer unit, and the other branch being a global exposure transfer unit; in the present embodiment, the rolling exposure transfer unit is a rolling exposure transfer transistor RTX, and the second terminal of the photodiode pd is coupled to the floating diffusion node FD through the rolling exposure transfer transistor RTX. The global exposure transfer unit includes a global exposure transfer transistor GTX, an exposure control transistor SSG, and a storage capacitor Cm, a second terminal of the photodiode pd is connected to a first terminal of the exposure control transistor SSG, a second terminal of the exposure control transistor SSG is connected to a first terminal of the global exposure transfer transistor GTX, a second terminal of the global exposure transfer transistor GTX is connected to the floating diffusion node FD, one terminal of the storage capacitor Cm is connected to a second terminal of the exposure control transistor SSG, and the other terminal thereof is connected to a gate of the exposure control transistor SSG. The first terminal of the photodiode pd is connected to a ground terminal, and specifically, the first terminal of the photodiode pd is an anode terminal and the second terminal thereof is a cathode terminal.
The reset transistor RST is coupled between a first voltage source Vrab and the floating diffusion node FD; the first voltage source Vrab is an independent voltage source. Specifically, the first voltage source Vrab is a variable voltage source.
The pixel structure of the image sensor further comprises an output unit, wherein the output unit is coupled to the floating diffusion node FD and is used for amplifying and outputting a voltage signal of the floating diffusion node FD. In the present embodiment, the output unit includes a source follower transistor SF having a gate coupled to the floating diffusion node FD, a drain coupled to a second voltage source, specifically, a fixed voltage source PIXVDD, and a source coupled to the column output line pix _ out through the row select transistor ROWSEL. Of course, the present embodiment only schematically shows one implementation manner of the output unit, and those skilled in the art should realize that the output unit may also include only the source follower transistor SF and not include the row selection transistor ROWSEL, and may also use other amplifying devices with different gains instead of the source follower transistor SF, for example, two-stage or multi-stage amplifiers may be used instead of the source follower transistor SF in the present embodiment, and these variations are within the protection scope of the present invention.
In the present embodiment, the storage capacitor Cm is a separate capacitance device. In the present embodiment, the reset transistor RST, the rolling exposure transfer transistor RTX, the global exposure transfer transistor GTX, the exposure control transistor SSG, and the row selection transistor ROWSEL are all NMOS, which allows for fast carrier mobility of the NMOS, so that the response speed of the switch is fast.
The reset transistor RST receives a reset control signal RST, the rolling exposure transfer transistor RTX receives a control signal RTX, the global exposure transfer transistor GTX receives a control signal GTX, the exposure control transistor SSG receives a control signal SSG, and the row selection transistor ROWSEL receives a row selection control signal ROWSEL.
The hybrid exposure mode is, for example, a rolling exposure and global exposure alternating exposure mode.
The following describes the principle of the pixel structure HDR based on the knee point in detail:
assuming that the voltage value of the control signal RTX during the exposure period is V1, where V1 is greater than zero but slightly smaller than the threshold voltage of the rolling exposure transfer transistor RTX, when the accumulated charges of the photodiode pd gradually increase and the voltage at the terminal of the photodiode pd decreases to a certain voltage, the rolling exposure transfer transistor RTX operates in the sub-threshold state, generating the sub-threshold current flowing to the photodiode pd.
When the photocurrent of the photodiode pd is equal to the subthreshold current and the light intensity is not changed, the charge accumulated on the photodiode pd will remain unchanged, so that the rtx signal is controlled during the exposure period of the photodiode pd, which not only can prevent the overexposure (blooming) phenomenon caused by the over-strong light intensity, but also the value of the charge in the well will change with the change of the balance current and the light intensity, thereby the pixel structure can realize the high dynamic range characteristic.
Specifically, the timing control of the rtx signal during the exposure process can be, for example, as shown in fig. 2a, the exposure period is defined as the period from the start of integration to the end of integration, during the exposure (exposure), the rtx signal is controlled in segments, for example, in three segments, so that the rtx signal is gradually reduced to a relatively low voltage NVDD in three segments from a relatively high voltage TXVDD during the exposure period, specifically, for example, the rtx signal is controlled to a relatively high voltage TXVDD before the start of exposure, during the first exposure time t1, the rtx signal is controlled to a first voltage V1, during the second exposure time t2, the rtx signal is controlled to a second voltage V2, and during the third exposure time t3, the rtx signal is controlled to a relatively low voltage NVDD; further, the RST signal is controlled to be high level throughout the exposure period, so that the reset transistor RST is turned on, the potential of the floating diffusion node FD is pulled up to the voltage of the first voltage source Vrab, that is, the drain voltage of the rolling exposure transfer transistor RTX is pulled up to the voltage of the first voltage source Vrab, and the first voltage source Vrab is controlled to be a relatively high voltage throughout the exposure period. Assuming that the total exposure time is a fixed value, the curve of the output signal with the light intensity obtained by such exposure control as shown in fig. 2a is shown in fig. 2b, wherein the solid line in fig. 2b represents the curve obtained by using the exposure control of fig. 2a, and the dotted line represents the curve obtained by using the conventional exposure method, as can be seen from fig. 2b, the value of the full well charge of the pixel is increased by controlling the rtx signal during the exposure. Where solid curves pixel 1, pixel 2, pixel 3 indicate that the position of the output curve at the inflection point will vary due to process fluctuations. Of course, it should be appreciated that the control scheme of fig. 2a is merely an example, the control of the rtx signal is not limited to three segments, other numbers of segments may be used, and the control time of each segment is not fixedly limited.
The pixel structure of the HDR image sensor based on the inflection point provided by the present invention can work in different exposure modes, such as a rolling exposure mode, a global exposure mode and a hybrid exposure mode, and the following describes in detail the working principle of the pixel structure provided by the present invention in the global exposure mode and the rolling exposure mode.
1. Global exposure mode
In this mode, the pixel array is exposed at the same time and read row by row, and the timing control is as shown in fig. 3, and the specific working process is as follows:
1) circuit and pd reset
a. Setting RST, RTX and GTX to high potential, conducting corresponding transistors RST, RTX and GTX, and initializing a floating diffusion node FD, a photodiode pd and a storage capacitor Cm to Vrab voltage;
b. RST, RTX and GTX are set to low levels, corresponding transistors RST, RTX and GTX are turned off, SSG is set to high levels, an exposure control transistor SSG is turned on, and initialization potentials of a storage capacitor Cm and a photodiode pd are balanced.
2) Exposure method
c. Setting SSG to low level, turning off the exposure control transistor SSG, controlling rtx voltage in 2 segments, as shown in fig. 3, starting exposure and charge accumulation by the photodiode pd, changing SSG to high level before the exposure is finished, transferring the charge accumulated by the photodiode pd to the storage capacitor Cm, then changing SSG to low level again, turning off the exposure control transistor SSG, and ending the exposure.
3) Reading
d. Setting rowsel to high level, gating reading row output, setting RST to low level, turning off a reset transistor RST, and reading an initial potential V0;
e. setting gtx to a high level, and transferring the charge stored in the storage capacitor Cm to the floating diffusion node FD;
f. reading the output voltage value V1 at the moment;
g. setting RTX as high level, turning on a rolling exposure transmission transistor RTX, setting RST as high level, turning on a reset transistor RST, and resetting a pd end of a photodiode to Vrab potential;
h. setting Vrab as a low level, changing RTX into an inflection point voltage Vknee, enabling the electric charge at the pd end of the photodiode to be a value when an inflection point exists, then enabling RTX to be a low level, and completely turning off a rolling exposure transmission transistor RTX;
i. setting RST to be high level, turning on a reset transistor RST, and resetting the pd end of the photodiode to be Vrab potential again;
j. setting RST to be low level, turning off a reset transistor RST, and reading an output value Vk0 at the moment;
k. setting RTX to be high level, turning on the rolling exposure transfer transistor RTX, and transferring the charge accumulated by the photodiode pd to the floating diffusion node FD;
let RTX be low, turn off the rolling exposure transfer transistor RTX, and read the output voltage value Vk1 at this time.
By performing two correlation operations on V0, V1, Vk0 and Vk1, respectively, the obtained photo signals Vsig is V1-V0, and Vk is Vk1-Vk0, where Vk is the actual knee voltage value of each pixel output curve, and performing operation processing on Vsig and Vk can obtain an image with a high dynamic range for knee correction, where the operation processing is performed by using an existing operation processing method, which is not described in detail herein.
2. Rolling exposure mode
In this mode, the pixel array is exposed and read line by line, and the timing control is as shown in fig. 4, and the specific working process is as follows:
1) circuit and pd reset
a. Setting RST, RTX and GTX to high potential, conducting corresponding transistors RST, RTX and GTX, and initializing a floating diffusion node FD, a photodiode pd and a storage capacitor Cm to Vrab voltage;
b. RST, RTX and GTX are set to low levels, corresponding transistors RST, RTX and GTX are turned off, SSG is set to high levels, an exposure control transistor SSG is turned on, and initialization potentials of a storage capacitor Cm and a photodiode pd are balanced.
2) Exposure method
c. SSG is set to low level, the exposure control transistor SSG is turned off, and the rtx voltage is controlled in 2 segments, as shown in fig. 4, and the photodiode pd starts to expose and accumulate charges.
3) Reading
d. Setting rowsel to high level, gating reading row output, setting RST to low level, turning off a reset transistor RST, and reading an initial potential V0;
e. setting rtx to high level, and transferring the charges accumulated in the photodiode pd to the floating diffusion node FD;
f. reading the output voltage value V1 at the moment;
g. setting RTX as high level, turning on a rolling exposure transmission transistor RTX, setting RST as high level, turning on a reset transistor RST, and resetting a pd end of a photodiode to Vrab potential;
h. setting Vrab as a low level, changing RTX into an inflection point voltage Vknee, enabling the electric charge at the pd end of the photodiode to be a value when an inflection point exists, then enabling RTX to be a low level, and completely turning off a rolling exposure transmission transistor RTX;
i. setting RST to be high level, turning on a reset transistor RST, and resetting the pd end of the photodiode to be Vrab potential again;
j. setting RST to be low level, turning off a reset transistor RST, and reading an output value Vk0 at the moment;
k. setting RTX to be high level, turning on the rolling exposure transfer transistor RTX, and transferring the charge accumulated by the photodiode pd to the floating diffusion node FD;
let RTX be low, turn off the rolling exposure transfer transistor RTX, and read the output voltage value Vk1 at this time.
Normally, V0 and V1, Vk0 and Vk1 are respectively subjected to two correlation operations, the obtained photo signals Vsig is V1-V0, and Vk is Vk1-Vk0, where Vk is an actual knee voltage value of each pixel output curve, and Vsig and Vk are subjected to an operation process to obtain an image with a high dynamic range for knee correction, where the operation process is performed by using an existing operation processing method, which is not described in detail herein.
In the hybrid exposure mode, referring to the principle of the global exposure mode and the rolling exposure mode, in the exposure process, the rolling exposure transfer transistor RTX and the exposure control transistor SSG are alternately turned on, so that a part of the charge accumulated in the photodiode pd is transferred to the floating diffusion node through the rolling exposure transfer transistor RTX, and the other part is transferred to the storage capacitor Cm through the exposure control transistor SSG; the subsequent reading process can refer to the reading in the global exposure mode and the rolling exposure mode.
Example 2
Referring to fig. 5, as shown in fig. 5, compared to embodiment 1, in the HDR image sensor pixel structure based on knee point provided by the embodiment of the present invention, the storage capacitor Cm is a parasitic capacitance, specifically, the storage capacitor Cm is a parasitic capacitance of the exposure control transistor SSG to ground. Otherwise, other aspects of this embodiment are the same as embodiment 1, and are not described herein again.
Example 3
Referring to fig. 6, as shown in fig. 6, the present embodiment provides an imaging system 100, including a pixel array 110, where the pixel array 110 is arranged in rows and columns, a structure of each pixel in the pixel array 110 may be any one of the pixel structures in embodiments 1 to 2, and for a specific case of the pixel structure, reference is made to embodiments 1 to 2, which is not repeated herein.
In addition, as an exemplary embodiment, the imaging system further includes a logic control unit 120, a driving unit, a column a/D conversion unit 150, and an image processing unit 160; wherein:
the logic control unit 120 is used for controlling the working sequential logic of the whole system;
one end of the driving unit is connected to the logic control unit 120, and the other end of the driving unit is coupled to the pixel array 110, and is used for driving and controlling each control signal line in the pixel array 110; specifically, the driving unit includes a row driving unit 130 and a column driving unit 140, one end of the row driving unit 130 is connected to the logic control unit 120, and the other end is coupled to the pixel array 110, for providing a corresponding row control signal to the pixel array 110; one end of the column driving unit 140 is connected to the logic control unit 120, and the other end is coupled to the pixel array 110, and is configured to provide a corresponding column control signal to the pixel array 110;
the column a/D conversion unit 150 corresponds to each column of pixels in the pixel array 110, and is configured to implement analog/digital conversion of column signals under the control of the logic control unit 120;
the image processing unit 160 is configured to perform image processing on the image digital signals output by the column a/D conversion unit 150 under the control of the logic control unit 120.
It will be apparent to those skilled in the art that various changes and modifications may be made in the invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (22)
1. An inflection point based HDR image sensor pixel structure, comprising:
a photodiode for accumulating charges generated by a photoelectric effect in response to incident light;
a reset transistor coupled between a first voltage source and the floating diffusion node for resetting a voltage of the floating diffusion node according to a reset control signal;
a rolling exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the rolling exposure transmission unit is used for providing balance current to control full-trap charges in the exposure process of the photodiode, works in a subthreshold state along with the gradual reduction of the terminal voltage of the photodiode, generates subthreshold current flowing to the photodiode, keeps the charges accumulated by the photodiode unchanged, and accordingly changes the transmission gain; and for transferring charge accumulated by the photodiode to the floating diffusion node in a rolling exposure mode or a hybrid exposure mode;
a global exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the global exposure transmission unit is used for storing the electric charge accumulated by the photodiode in the exposure process of a global exposure mode or a mixed exposure mode and transferring the stored electric charge to the floating diffusion node after the exposure is finished;
and the output unit is coupled to the floating diffusion node and used for amplifying and outputting the voltage signal of the floating diffusion node.
2. The knee-based HDR image sensor pixel structure of claim 1, wherein the rolling exposure transfer unit comprises a rolling exposure transfer transistor through which the photodiode is coupled to the floating diffusion node.
3. The knee-based HDR image sensor pixel structure of claim 2, wherein the rolling exposure pass transistor is configured to operate in a sub-threshold state as the terminal voltage of the photodiode decreases gradually during the exposure of the photodiode to supply current to the photodiode to balance the photocurrent so that the terminal voltage of the photodiode remains constant.
4. The corner-based HDR image sensor pixel structure of any of claims 1 to 3, wherein the global exposure transfer unit comprises a global exposure transfer transistor, an exposure control transistor, and a storage capacitor, the photodiode being coupled to the floating diffusion node through the exposure control transistor and the global exposure transfer transistor, the storage capacitor having a first terminal coupled to a node between the exposure control transistor and the global exposure transfer transistor and a second terminal coupled to a gate or a ground of the exposure control transistor or to a fixed voltage value.
5. The knee-based HDR image sensor pixel structure of claim 4, wherein the storage capacitor is a separate capacitive device or is a parasitic capacitance of the exposure control transistor.
6. The knee-based HDR image sensor pixel structure of claim 1, wherein the hybrid exposure mode is a rolling exposure and global exposure alternating exposure mode.
7. The knee-based HDR image sensor pixel structure of claim 1, wherein the first voltage source is a variable voltage source.
8. The knee-based HDR image sensor pixel structure of claim 1, wherein the output unit comprises an amplifier coupled between a floating diffusion node and a column output line for amplifying and outputting a voltage signal of the floating diffusion node.
9. The corner-based HDR image sensor pixel structure of claim 8, wherein the amplifier is a source follower transistor having a gate coupled to the floating diffusion node, a drain coupled to a second voltage source, and a source coupled to a column output line.
10. The knee-based HDR image sensor pixel structure of claim 8 or 9, wherein the output cell further comprises a row select transistor through which the amplifier is coupled to a column output line.
11. An imaging system comprising an array of pixels arranged in rows and columns, each pixel in the array of pixels comprising:
a photodiode for accumulating charges generated by a photoelectric effect in response to incident light;
a reset transistor coupled between a first voltage source and the floating diffusion node for resetting a voltage of the floating diffusion node according to a reset control signal;
a rolling exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the rolling exposure transmission unit is used for providing balance current in the exposure process of the photodiode so as to control the full-trap charge quantity, and the rolling exposure transmission unit works in a subthreshold state along with the gradual reduction of the terminal voltage of the photodiode, generates subthreshold current flowing to the photodiode so as to keep the charge accumulated by the photodiode unchanged and change the transmission gain; and for transferring charge accumulated by the photodiode to the floating diffusion node in a rolling exposure mode or a hybrid exposure mode;
a global exposure transfer unit through which the photodiode is coupled to the floating diffusion node; the global exposure transmission unit is used for storing the electric charge accumulated by the photodiode in the exposure process of a global exposure mode or a mixed exposure mode and transferring the stored electric charge to the floating diffusion node after the exposure is finished;
and the output unit is coupled to the floating diffusion node and used for amplifying and outputting the voltage signal of the floating diffusion node.
12. The imaging system of claim 11, further comprising a logic control unit, a driving unit, a column a/D conversion unit, and an image processing unit; wherein:
the logic control unit is used for controlling the working sequence logic of the whole system;
one end of the driving unit is connected with the logic control unit, and the other end of the driving unit is coupled with the pixel array and used for driving and controlling each control signal line in the pixel array;
the column A/D conversion unit corresponds to each column of pixels in the pixel array and is used for realizing analog/digital conversion of column signals under the control of the logic control unit;
the image processing unit is used for carrying out image processing on the image digital signals output by the column A/D conversion unit under the control of the logic control unit.
13. The imaging system of claim 12, wherein the driving unit comprises:
a row driving unit, one end of which is connected with the logic control unit and the other end of which is coupled with the pixel array, and is used for providing corresponding row control signals for the pixel array;
and the column driving unit is connected with the logic control unit at one end, is coupled with the pixel array at the other end and is used for providing a corresponding column control signal for the pixel array.
14. The imaging system of claim 11, wherein the rolling exposure transfer unit includes a rolling exposure transfer transistor through which the photodiode is coupled to the floating diffusion node.
15. The imaging system of claim 14, wherein the rolling exposure pass transistor is configured to operate in a sub-threshold state as the terminal voltage of the photodiode decreases during exposure of the photodiode to provide current to the photodiode to balance the photocurrent such that the terminal voltage of the photodiode remains constant.
16. The imaging system according to claim 11 or 15, wherein the global exposure transfer unit includes a global exposure transfer transistor, an exposure control transistor, and a storage capacitor, the photodiode being coupled to the floating diffusion node through the exposure control transistor and the global exposure transfer transistor, the storage capacitor having a first terminal coupled to a node between the exposure control transistor and the global exposure transfer transistor and a second terminal coupled to a gate of the exposure control transistor or a ground terminal or a fixed voltage value.
17. The imaging system of claim 16, wherein the storage capacitor is a separate capacitive device or is a parasitic capacitance of the exposure control transistor.
18. The imaging system of claim 11, wherein the hybrid exposure mode is a rolling exposure and global exposure alternating exposure mode.
19. The imaging system of claim 11, wherein the first voltage source is a variable voltage source.
20. The imaging system according to claim 11, wherein the output unit includes an amplifier coupled between a floating diffusion node and a column output line for amplifying and outputting a voltage signal of the floating diffusion node.
21. The imaging system of claim 20, wherein the amplifier is a source follower transistor having a gate coupled to the floating diffusion node, a drain coupled to a second voltage source, and a source coupled to a column output line.
22. The imaging system of claim 20 or 21, wherein the output cell further comprises a row select transistor, the amplifier being coupled to a column output line through the row select transistor.
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| CN109040628B (en) * | 2018-10-31 | 2020-12-08 | 锐芯微电子股份有限公司 | Image sensor pixel circuit and working method thereof |
| US11611813B2 (en) * | 2019-09-16 | 2023-03-21 | Shanghai Ic R&D Center Co., Ltd | Method of removing fixed pattern noise |
| CN111866414B (en) * | 2020-07-15 | 2021-08-20 | 大连理工大学 | High-dynamic image sensor pixel structure and time sequence control method |
| CN112004037B (en) * | 2020-09-03 | 2022-06-24 | 锐芯微电子股份有限公司 | Image sensor pixel structure |
| CN112040156B (en) * | 2020-09-15 | 2023-04-07 | 锐芯微电子股份有限公司 | Global exposure image sensor circuit and control method thereof |
| CN113055617B (en) * | 2021-05-08 | 2023-05-12 | 长春长光辰芯微电子股份有限公司 | Image sensor |
| CN114900687B (en) * | 2022-05-17 | 2024-03-05 | 中国科学院新疆理化技术研究所 | Simulation method for influence of different light intensities on full well capacity of pixel unit of CMOS image sensor |
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